We have studied the effects of intraventricularly administered kainic acid on hippocampal neurons. We have discovered that kainic acid destroys specific populations of hippocampal cells (CA4, CA3, CA1) but spares others (CA2, granule cells). The damage created in the hippocampus closely parallels that in man produced as a result of stroke, senile dementia and epilepsy. Axon sprouting and the formation of new synapses appears to take place and create a new circuitry in the damaged hippocampus. On the basis of present data, the reordering is highly specific depending on the nature of cell loss and the time after the lesion. Our results in rats may provide clues on the nature of synaptic reconstruction in man after hippocampal damage.